Nibbling punch

ABSTRACT

A nibbling punch including a body with a downwardly projecting heel around its lower end to embed in the upper portion of a workpiece to prevent lateral sliding of the punch as the latter is driven through the workpiece. In operations where the workpiece is manually indexed relative to the punch, a pilot punch is connected to the nibbling punch to act as a locater and to determine the extent of the next bite made by the nibbling punch.

United States Patent 1 Pfleiderer et al.

[ 1 Apr. 24,1973

[ 1 NIBBLING PUNCH [75] Inventors: George Pfleiderer, Rockford; Eu-

gene H. Paquet, Winnebago, both of [11.

[73] Assignee: W. A. Whitney Corp., Rockford, Ill.

[22] Filed: Oct. 12, 1970 [21 Appl. No.: 79,986

[52] U.S. Cl. ..83/621, 83/622, 83/688,

83/693, 83/916 [51] Int. Cl. ..B26f 1/14 [58] Field of Search ..83/9l6, 237, 249,

[56] References Cited UNITED STATES PATENTS Wilson ..83/916 X ..83/916 X Clark ..83/686 X 6/1934 Chenette 4/1972 Primary ExaminerFrank T. Yost AttorneyWolfe, Hubbard, Leydig, Voit 8L Osann, Ltd.

57 ABSTRACT A nibbling punch including a body with a downwardly projecting heel around its lower end to embed in theupper portion of a workpiece to prevent lateral sliding of the punch as the latter is driven through the workpiece. In operations where the workpiece is manually indexed relative to the punch, a pilot punch is connected to the nibbling punch to act as a locater and to determine the extent of the next bite made by the nibbling punch.

1 Claim, 10 Drawing Figures PAIENIEDAPRMIHB 3.728.927

SHEETBUFZ I NIBBLING PUNCH BACKGROUND OF THE INVENTION This invention relates to a punch adapted to coact with an underlying die to form a hole in an intervening workpiece. More particularly, the invention relates to a nibbling punch for forming a hole which is larger than the punch itself. In a nibbling operation, the punch bites off successive strips of material with a punching action to form a slot around the periphery of the large hole to be formed, the slot eventually extending around the entire periphery to free a central slug of material and form the large hole. As each strip is punched from the end of the slot, a portion of the nibbling punch overhangs the slot without engaging the workpiece. As a result, the punch tends to slide laterally on the workpiece and move out of alinement with the die. If allowed to slide, the punch will impact against the die and will shear the cutting edge of the punch, the die or both.

SUMMARY OF THE INVENTION The general aim of the present invention is to provide a simplified and comparatively inexpensive nibbling punch which acts to restrict itself against lateral sliding relative to the workpiece and the die without need of being interlocked with the die to keep the two in alinement.

A related object is to achieve the foregoing through the provision of a punch which is operable to bite into and embed in the upper portion of the workpiece at the start of the punching operation so as to lock itself against sliding laterally of the workpiece and out of alinement with the die.

The invention is particularly characterized by the formation of a recess within the lower end of the punch to form a downwardly projecting heel around the punch. During punching, the heel first embeds in the upper portion of the workpiece and then coacts with the downwardly facing surface of the recess to shear the workpiece cleanly around the peripheral edge of the heel.

A further object of the invention is to provide the nibbling punch with a detachable pilot punch which may be used optionally with the nibbling punch to control the extent of the bite taken by the nibbling punch, the pilot punch being uniquely located relative to the heel.

Other objects and advantages will become apparent from the following detailed description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a fragmentary side elevation of an exemplary punch press equipped with a new and improved nib-v bling punch embodying the novel features of the present invention. A

FIG. 2 is a perspective view ofa workpiece showing a slot formed by nibbling partially around the periphery ofa large hole to be punched.

FIG. 3 is an enlarged fragmentary cross-section taken substantially along the line 33 of FIG. 1.

FIG. 4 is an enlarged end view of the nibbling punch shown in FIG. 3.

FIG. 5 is an enlarged partial cross-section similar to FIG. 3 and, in addition, showing a portion of a workpiece with the nibbling punch partially embedded in the upper portion thereof.

FIG. 6 is an enlarged partial cross'section similar to FIG. 5 but showing parts in moved positions.

F IG. 7 is an enlarged fragmentary cross-section similar to FIG. 3 but showing a pilot punch attached to the nibbling punch.

F IG. 8 is an enlarged end view of the nibbling punch and pilot punch shown in FIG. 7.

FIG. 9 is an enlarged partial plan view of the workpiece as shown in FIG. 2'with the pilot punch abutting the edge of the slot to limit the bite of the nibbling punch.

FIG. 10 is an enlarged end view showing a nibbling punch with a square cross-section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in the drawings for purposes of illustration, the invention is embodied in a nibbling punch for use in a punch press 16 and adapted to coact with an underlying die 19 to form a hole 20 in a sheet metal workpiece 21 disposed between the punch and the die. Herein, the press includes a frame 22 mounted on a bed 23 and supporting a hydraulic cylinder 24 whose ram 25 is operable to reciprocate the nibbling punch through downward and upward strokes relative to the die, the latter also being supported on the frame.

The punch 15 includes a cylindrical body 26 (FIG. 3) with a circular-shaped lower end which is operable to be punched through the workpiece 21. At the upper end of the body is an annular shoulder 29 with an upwardly extending shank 30 telescoped into a punch holder 31 on the lower end of the ram 25 and held therein by a set screw 32. As the ram is reciprocated, the punch cooperates with the die 19 to perform a nibbling operation on the workpiece.

Nibbling is a punching operation which involves taking partial bites of material around the periphery of the hole 20 (FIG. 2) to be formed so as to cut an elongated slot 20a whose ends eventually meet to free a large central slug 33 from the workpiece and thereby form the hole 20. Thus, during an exemplary nibbling operation, a small circular hole (not shown) is first punched at the edge of the larger hole 20 to be formed and then the workpiece is shifted or indexed to position a portion of the punch 15 over the edge of the small hole for the first partial bite. Thereafter, the workpiece is indexed step-by-step to successively position the punch around the periphery of the large hole 20 to be formed so that, on each downward stroke, the punch takes partial bites at the edge of the previously formed hole. Thus, the elongated slot 20a shown in FIG. 2 is gradually formed and eventually closes on itself to free the central slug 33 and form the larger hole 20. During each bite, a portion of the punch necessarily overhangs the slot 20a without engaging the workpiece as shown in FIG. 5

' and, as a result,.the punch has a tendency to slide The present invention contemplates preventing lateral movement of the punch 15 on the workpiece 21 and relative to the die 19 by embedding the punch in the upper portion of the workpiece in a novel manner as the ram 25 first forces the punch into engagement with the workpiece. For this purpose, the punch is formed with a downwardly projecting heel 34 (FIG. by cutting a downwardly opening recess 35 of predetermined size in the lower end of the body 26. When the punch is driven into the workpiece (FIG. 5), the heel bites into and embeds in the upper portion of the workpiece and locks the punch against lateral sliding. When the heel is completely embedded (FIG. 6), the top wall or upper surface 36 of the recess contacts the upper surface of the workpiece and coacts with a peripheral cutting edge 39 on the heel to shear the workpiece. As a result of locking the punch directly to the workpiece, the punch is restricted from sliding laterally on the workpiece and thus remains in alinement with the die 19 during the downward stroke of the ram without need of being interlocked physically with the die to maintain such alinement.

In the embodiment shown in FIGS. 1 to 6, the heel 34 is annular, is concentrically disposed relative to the center line of the punch 15, and is formed around the periphery of the lower end of the body 26. As pointed out above, the heel is formed by carving out the central portion of the lower end of the body in an inverted dish shape to fashion the circular recess 35, the latter preferably being shallower than the thickness of the workpiece and including the generally horizontal upper surface 36. Accordingly, the heel comprises an upwardly extending inner wall 41 defining the side wall of the recess, a bottom surface 43, and an outer wall 44 which is vertically alined with the outer wall 45 of the body 26, the surface 43 intersecting with the outer wall to define the cutting edge 39 and with the inner wall 41 to define a sharp lower edge 39a.

Thus, as the ram 25 advances, a portion of the heel 34 embeds in the workpiece 21 so that the inner wall 41 locks against a complementary wall 46 in the workpiece to resist lateral movement of the punch relative to the die 19, the wall 46 being formed as an incident to initial penetration of the heel into the workpiece. The locking of the narrow heel with the workpiece takes place before the larger upper surface 36 of the recess 35 engages the workpiece and creates a force tending to cause sliding. Once the heel is completely seated in the upper portion of the workpiece as shown in FIG. 6, the cutting edge 39, which is formed at the junction of the bottom surface 43 and the outer wall 44, coacts with the upper surface of the recess and the die as the ram continues to advance to punch a strip 47 (FIG. 9) of material from the edge of the slot a. After the punch has been advanced through the workpiece, the ram is retracted to pull the lower end of the punch above the workpiece so that the latter may be indexed for the next bite.

One method used to index the workpiece 21 during the nibbling operation involves the use of a numerically controlled positioning system which automatically indexes the workpiece for each step. With this method, the extent of each bite to be taken by punch 15 as well as the path to be followed by the workpiece is automatically established and the indexing is achieved by power-actuated positioning means (not shown). Another method which is used involves manually indexing the workpiece. With this latter method, the operator of the press usually moves the workpiece into a proper position under the punch and uses a template or other means to determine the path which should be followed.

To facilitate manual indexing of the workpiece 21, the present invention contemplates the provision of a pilot punch 50 (FIG. 7) which may be used optionally with the nibbling punch 15 during the nibbling operation to determine the extent of each bite taken by the nibbling punch. For this purpose, the pilot punch is connected to the body 26 in unique relation to the heel 34 and extends below the lower end of the body to act as a locater. On the first stroke of the ram 25, the pilot punch punches through the workpiece ahead of the nibbling punch and forms a small but complete hole in the workpiece just before the nibbling punch forms a slightly larger hole. Thereafter, the workpiece is indexed until the edge of the slot 20a engages the periphery of the pilot punch to determine the extent of the next bite. The ram is then actuated to shear the strip 47 of material from the workpiece (FIG. 9), thus completing one step of the nibbling operation.

In the preferred instance, the pilot punch 50 comprises a cylindrical member in the form of a head piece 51 (FIG. 7) centered on one end of a cylindrical base portion 53 whose other end is connected to a threaded shank 54. To attach the pilot punch to the nibbling punch, the shank is threaded into a hole drilled upwardly from the upper surface 36 of the recess 35 and into the punch body 26. A set screw 55 extending radially through the body engages the shank to help anchor the pilot punch rigidly to the body. When the shank is completely threaded into the hole, the upper surface 56 of the base portion abuts the upper surface of the recess to provide support for the headpiece.

The headpiece 51 extends below the lower end of the body 26 as shown in FIG. 7 and includes a substantially vertical locater wall 59 of the same general shape as the wall 45 of the body. A sharp cutting edge 60 is formed around the lower end of the wall 59. Accordingly, during the initial portion of the first downward stroke of the ram 25, the edge 60 acts to punch a first hole (not shown) in the workpiece. With continued advance of the ram, the nibbling punch 15 embeds completely around the first hole and punches out a ring of material (not shown) from the periphery thereof. Thus, the pilot punch and nibbling punch act to give a double punching effect on the first downward stroke of the ram. Thereafter, the workpiece is indexed until the locater wall 59 engages the edge of the previously formed hole, i.e., the edge of the slot 20a. This correctly positions a portion of the lower end of the nibbling punch over the strip 47 (FIG. 9) of material to cut from the workpiece on the next advance of the ram.

To obtain the full effect of the heel 34 embedding into the workpiece 21, the diameter of the headpiece 51 should be somewhat less than the diameter of the recess 35. This leaves a radial gap between the locater wall 59 and the inner wall41 of the heel so that the latter may lock against the complementary wall 46 formed in the upper portion of the workpiece. Pilot punches of different diameters may be used to vary the width of the strip 47 punched out by the nibbling punch 15 but, in all cases, the pilot punch preferably should be kept sufficiently small such that the outer wall 59 thereof is located radially inwardly of the inner wall 41 of the heel 34.

Although the nibbling punch 15 has been described as being formed with a circular cross-section, it will be recognized that the novel features of the present invention can be incorporated in punches of various crosssectional shapes. For instance, a punch 15' incorporating those features is shown in FIG. and is formed with a square cross-section and with a square heel 34'. To simplify machining, the square-shaped nibbling punch is formed with a generally circular recess 35 rather than being formed with a square recess corresponding to the shape of the heel.

From the foregoing, it will be apparent that the new and improved nibbling punch 15 of the present invention is operable to prevent lateral sliding of the punch as it is driven downwardly against the workpiece 21. This is accomplished by the heel 34 which embeds in the upper portion of the workpiece to lock against the complementary wall 46 and hold the punch against lateral movement. The present invention is also of particular advantage in that it may be provided with the pilot punch 50 to facilitate manual indexing of the workpiece or used without the pilot punch when the workpiece is automatically indexed.

We claim:

1. A nibbling punch for use with an underlying die and operable on successive downward strokes to nibble out a large hole in an intervening workpiece adapted to be indexed laterally relative to the punch and die after each stroke, said punch comprising an upright body formed with a vertically extending outer wall, a sharp cutting edge formed on the extreme lower end of said wall around the entire outer periphery thereof, a downwardly opening and centrally located recess of inverted dish shape formed in the lower end of said body, said recess being defined by a top wall and by an upwardly extending side wall having a sharp lower edge spaced inwardly of said cutting edge, a heel defined by the outer wall of said body, the side wall of said recess and a substantially horizontal bottom surface which intersects with said side wall to define said lower edge and with said outer wall to define said cutting edge, said heel projecting downwardly from the top wall of said recess and extending completely around said body and being operable during each downward stroke to bite into and embed in the workpiece to lock the punch against lateral sliding on the workpiece and to keep said cutting edge alined laterally with said die, a pilot punch carried by said body for punching an initial hole in said workpiece and thereafter for locating said workpiece relative to said cutting edge when the workpiece is indexed relative to the nibbling punch, said pilot punch including an upright member connected to and projecting downwardly from the lower end of said body and formed with an outer wall which is shaped similarly to the outer wall of said body and located inwardly of said heel, an upper surface on said member seated against the top wall of said recess to support said member against movement upwardly relative to said body, and a cutting edge formed on the extreme lower out the initial hole in said workpiece. 

1. A nibbling punch for use with an underlying die and operable on successive downward strokes to nibble out a large hole in an intervening workpiece adapted to be indexed laterally relative to the punch and die after each stroke, said punch comprising an upright body formed with a vertically extending outer wall, a sharp cutting edge formed on the extreme lower end of said wall around the entire outer periphery thereof, a downwardly opening and centrally located recess of inverted dish shape formed in the lower end of said body, said recess being defined by a top wall and by an upwardly extending side wall Having a sharp lower edge spaced inwardly of said cutting edge, a heel defined by the outer wall of said body, the side wall of said recess and a substantially horizontal bottom surface which intersects with said side wall to define said lower edge and with said outer wall to define said cutting edge, said heel projecting downwardly from the top wall of said recess and extending completely around said body and being operable during each downward stroke to bite into and embed in the workpiece to lock the punch against lateral sliding on the workpiece and to keep said cutting edge alined laterally with said die, a pilot punch carried by said body for punching an initial hole in said workpiece and thereafter for locating said workpiece relative to said cutting edge when the workpiece is indexed relative to the nibbling punch, said pilot punch including an upright member connected to and projecting downwardly from the lower end of said body and formed with an outer wall which is shaped similarly to the outer wall of said body and located inwardly of said heel, an upper surface on said member seated against the top wall of said recess to support said member against movement upwardly relative to said body, and a cutting edge formed on the extreme lower end of the outer wall of said member and extending around the entire outer periphery thereof for punching out the initial hole in said workpiece. 